The present invention relates to bolting arrangements wherein two flanges are bolted together. More particularly, the present invention relates to bolting arrangements in which bolt bending resulting from relative movement of the flanges is minimized.
Flanges are generally bolted together by inserting bolts through bolt holes provided in each of the flanges and that are aligned with each other. Such bolted flanges usually remain in their bolted condition, because a number of connecting bolts are generally provided to securely hold the bolted flanges together. However, the imposition of large radial, tangential, or axial loads on one or both components to which the respective flanges are secured can impose on the connecting bolts bending moments or tensile forces that can cause deformation or rupture of the bolts.
For example, unusual and sometimes large loads can be applied to bolted flanges in turbomachines, where pairs of flanged end casings are commonly bolted together. In aircraft gas turbine engines that have axial flow fans or axial flow compressors, rotor blade failures, which can be caused by foreign object damage to fan or compressor blades resulting from foreign objects that are drawn into the fan or compressor, can cause rotor unbalance conditions. Such rotor unbalance conditions can impose radial, circumferential, and possibly also axial loads that can shift the positions of the flanges radially relative to each other, circumferentially relative to each other, or axially relative to each other. In either event, unintended high shear, bending, or tensile loads, or a combination of such loads, can be applied to the flange connecting bolts, leading to bolt deformation, and possibly to bolt rupture and separation of the bolted casings from each other. Casing separation at the bolted flanges is an undesirable condition, and the present invention is directed to avoiding flange bolt failures by minimizing bending and axial stresses imposed on flange connecting bolts when the flanges are subjected to relative movement with respect to each other as a result of external loads applied to the components to which the flanges are connected.